Computer systems equipped with clusters of communication controllers for providing network connections of the computer systems with external computer systems is a well-known computer configuration. For instance, this configuration may be used for storage systems providing data storage/exchange services to external computer systems. In this case, communication controllers provide the network connections of the external computer systems to internal storage media of the storage computers. Upgrade or any other modifications of the communication controllers are very critical for the operation of such computer systems, because these operations cause all network connections provided by the communication controller to be disconnected when such a modification is started. As a result, these network connections have to be reestablished using other communication controllers. Despite rapid development of computer technologies, there are a number of communication protocols/network protocols used for network connections which are not failover tolerant. This means that when the network connection established by the external computer system with the computer system using a failover non-tolerant network protocol is disconnected by the computer system, the external computer system will experience an I/O error. As usual, these I/O errors have to be recovered manually by users of the external computer systems. Thus, maintenance works on the clusters of the communication controllers of such computer systems may cause substantial disturbances in operation of the external computer systems having network connections with the computer systems.